The present invention relates to a lens for use in photography, and more particularly to a compact lens suitable for use in a camera having a simple construction with good imaging performance even at perimeter field angles. In recent years, leisure cameras which are lightweight, portable and inexpensive have been strongly desired and, accompanying this, lenses have been required which are compact and yet inexpensive and of high performance.
Development of a photographic lens that has a long focal length and is relatively inexpensive has been conducted previously. For example, a lens having a three-group structure known as a triplet has long been known to be an inexpensive lens. A lens having a triplet structure has a certain level of performance that is well-matched with the performance required of a camera, so such a lens is widely used in cameras. However, when the ratio of the overall lens length (defined as the on-axis distance from the lens element surface nearest an object side to the image plane of the compact lens) divided by the focal length of the compact lens becomes larger than 1.1, the curvature of field becomes too large, the imaging performance at perimeter field angles deteriorates, and it becomes difficult to satisfy the demand for a high performance lens.
On the other hand, numerous lenses of the telephoto type with a positive refractive power that have been advanced have been known as photography lenses with a short overall lens length, such as the one disclosed in Japanese Laid-Open Patent Publication 5-2204. However, the aspherical nature of these lenses is strong because the positive refractive power needs to be strong, resulting in there being room for improvement in imaging performance with respect to spherical aberration, coma, distortion, and lateral color. Thus, obtaining high performance with telephoto-type lenses is difficult.
In addition, lenses having four-element structures have generally been useful in correcting aberrations, but the their cost is higher than that of the above-described triplet.